Periodic Reporting for period 2 - PAMSEQ (High-Throughput Mapping of Antibody Sequences to Antigen Specificity in Placental Malaria)
Reporting period: 2023-07-01 to 2024-06-30
Placental malaria (PM) is a severe malaria complication in pregnancy, in areas with stable parasite transmission. It is a major cause of disease and death among pregnant women and their offspring. PM mainly affects primigravidae, as immunity is developed over successive pregnancies. This naturally acquired protection to PM is mediated by antibodies targeting a parasite antigen called VAR2CSA. Although VAR2CSA is a variable antigen, it has been previously demonstrated that the naturally acquired antibody response is generally broadly cross-reactive (meaning that serum from a multigravidae woman can recognize multiple VAR2CSA variants). However, the results of recently conducted trials of a VAR2CSA-based vaccine to prevent PM showed almost complete variant-specificity of the induced antibodies (only the particular VAR2CSA variant used for immunization was recognized), failing to mimic what occurs during natural infection. This research project aims to study in detail the specificity and sequence characteristics of VAR2CSA-specific antibodies generated during natural infection with the ultimate goal of discovering protective and conserved epitopes on VAR2CSA targeted by antibodies to guide future vaccine design.
During the outgoing phase of the project (18 months) work related to work packages 1 to 3 (sample collection, expression/purification of a panel of full-length VAR2CSA proteins and LIBRA-seq implementation) was successfully completed. The innovative technology (LIBRA-seq) was successfully applied to B cells isolated from African women with naturally acquired immunity to PM, allowing the identification of hundreds of antigen-specific human monoclonal antibodies. Strikingly, the great majority (86%) of the identified monoclonal are cross-reactive (recognizing more than one VAR2CSA variant) and around 50% block the binding of VAR2CSA to its receptor. The sequence information obtained allowed the production of a selected subset of 50 recombinant antibodies for further validation during the return phase of the project (12 months). The predicted reactivity of the subset of monoclonals has been verified both on recombinant antigens (by ELISA) and on native antigens expressed on the surface of parasite-infected erythrocytes (by flow cytometry). Epitope mapping has also been performed and the epitopes for some of the antibodies have been narrowed down to various regions of the target antigen.
The results of this project have been presented at two international conferences and included in a patent application.
The results of this project have been presented at two international conferences and included in a patent application.
The thorough characterization of the discovered antibodies has as major potential to accelerate the development of VAR2CSA-specific vaccines against PM, therefore having the potential to protect millions of malaria-exposed pregnant women.
Beyond a malaria-focused perspective, the knowledge generated by the project could also extend to other infectious diseases by opening up new avenues for the discovery of functional human monoclonal antibodies to then inform the design of better vaccines.
Beyond a malaria-focused perspective, the knowledge generated by the project could also extend to other infectious diseases by opening up new avenues for the discovery of functional human monoclonal antibodies to then inform the design of better vaccines.